- A very strange bug in macOS has just been discovered
- If a Mac is left on for (a little more than) 49 days, its networking functionality will completely fail
- Apparently the only cure is a reboot, but Apple will likely work on an official fix.
Have you ever wondered what would happen if you left your Mac on for a few months? Probably not, but you might be interested to learn that if you did, the networking side of the operating system would collapse.
Tom’s Hardware reports that Photon wrote a blog post explaining how it “found a time bomb in the macOS TCP network,” an explosive element in the code that “detonates after exactly 49 days.”
Well, 49 days, 17 hours, two minutes and 47 seconds to be precise. When macOS runs continuously for this exact amount of time, the operating system experiences an “integer overflow” which “freezes the internal TCP timestamp clock.”
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When this happens, existing TCP network connections will not time out as they should, remain frozen, and ultimately, as Photon explains: “Ephemeral ports slowly exhaust, and eventually no new TCP connections can be established. ICMP (ping) continues to work. Everything else dies.”
In short, networking on Mac becomes completely impossible and the only remedy is to restart the machine. Yes, the old “turn it off and on again” solution.
Photon, a company that makes it easier to create AI agents, discovered this bug on the Macs it uses to monitor Apple’s Messages service, and the company was able to reproduce the issue on two systems.
Obviously, this isn’t a problem that most of you – assuming you own a Mac – will need to worry about. No daily user leaves their machine on for 50 days; but in case you are ever inclined to do so, at least you are now warned. This is of course more of an issue that will affect servers (which run continuously for long periods of time) and one that companies like Photon need to be aware of.
The root cause of the problem is, as mentioned, an integer overflow. This is where macOS assumes that a counter will only increase in numerical value, when in fact it returns to zero after 50 days of increasing – and this is something that has also surprised Microsoft in the past. Photon reminds us that Windows 95 suffered a similar 49.7 day crash during which the kernel’s 32-bit millisecond tick counter overflowed, in this case causing the PC to crash completely.
Apparently, Photon is working on a solution to avoid having to restart in order to repair the Mac, but probably now that this bug has been brought to Apple’s attention, we should see an official fix shortly.
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